Proceedings of the Fifth Asian Regional Maize Workshop - Search ...

Table 5. Differences in net income between various cropping systems tested in southern Taiwan
(1986-1990).
Net Income (US$/ha)
Code Cropping systems Average
(US$/ha)
1986 1987 1988 1989 1990
R1 Rice-Soybean-Corn 3,727 1,121 2,899 3,868 1,976 2,716 a
R2 Rice-Sesbania-Corn 3,836 1,511 2,829 2,480 2,690 2,669 ab
R3 Sorghum-Soybean-Corn 4,603 1,009 2,691 3,113 1,031 2,490 b
level
Means followed by the same letter do not differ significantly at 0.05% probability
(DMRT).
5. Plant protection:
The most important insect pest in corn grain production in Taiwan is the Asian corn borer
O. furnaca7is Guenee. In southern Taiwan, there are 6-8 generations of corn borer. The damage
caused by this pest may be as high as 90%. In order to avoid corn borer damage, farmers usually
have to apply chemicals 5 to 7 times during the growing season. In order to reduce both the user
of insecticides and production costs, in 1984 the government implemented a biocontrol program
using mass releases of Trichogramma ostriniae (a parasitoid of corn borer egg masses) (Chen and
Chur, 1948) for reducing the corn borer damage. Under this program T. ostriniae was released in
approximately 16,000 ha each year (Taiwan Govmt. Annual Rept. 1985-1988). In order to produce
enough eggs of the parasitoid for practical use, three T. ostriniae propagation stations (Kung­
Fu, Potzu and Woo-Shu-Lin) were established in the period of 1984-1986 (Tseng, 1990). In
practice, T. ostriniae is released four times in each cropping season, at a rate of 75 egg
cards/ha (300,000-360,000 egg parasitoids/ha), in an interval of 8 days. The egg cards are fixed
to the underside of the leaves near the ears with a stapler. Three insecticide treatments are
applied at the early whorl, late whorl, and pollen-shedding stages (Fig. 3). (Tseng and Wu,
1990). The results from field experiments showed that the mass releases of T. ostriniae increased
the percentage of parasitism of egg masses by 8-20%, compared with areas where no
releases of egg parasitoids were made (Table 6). This integrated control gave 11% higher grain
yield than the conventional control (insecticide treatment applied from early whorl to pollenshedding
stages at an interval of 7-10 days) (Table 7).
Atil•••• of 'ga card.
tour tim....eh
Aftar
8 dly' .plrt
L~~-~~"~~;:~-+- 8 -+-~
I +0''''-... dlY. t -day'i
'!1
In..ctlclae
It..tmanl
2!!J1
In..ctlcld,
t,.atm,nt
3~.
Ina'cU~ld.
',..alm,nt
Sowing
Early.
whorl
• t.gl
lat. SlIklnG Pollan· BlI,tar
whorl .tage ,heddlng Itag•
Itagl
.tagl
Fig.3.
Steps adopted in the integrated control of the Asian corn borer on field corn.
125